Background:
Current HT receiver and speakers was a $300 big-box special. Although it sounded decent, the bass was lacking. Knowing I wanted a sub that could deliver subaudible content with confidence, I started looking for deals on Craigslist. Striking out with the dimensions and cost of these used subs, I changed my tack and start exploring this DIY forum. As much as I wanted to build a monster-sized dream sub with an 18” driver, I was constrained to use the open corner space behind the sectional sofa’s curve. Our living room is not that big and adding a freestanding sub to the existing floor plan would not satisfy the WAF (wife acceptance factor). Bounded by this corner space, I set out to design a wedge shaped enclosure that delivers audible and subaudible punch.

Design Phase:
I set a loose budget goal of $500 and started to design a ported sub enclosure between 4-6 Ft^3 air volume. Using WinISD Pro and AutoCAD I developed and evaluated different geometries, drivers and port sizing. Fast forward through 4 weeks of design iterations and I settled on a design that met my requirements.

Key Specs:

Wedge shaped enclosure, 5 cubic feet air volume, ~50” tall

Bass Reflex/Ported enclosure tuned to 20Hz

12” CSS Trio driver, down firing orientation

BASH 500w plate amp from Parts Express

Amp modified with an 18.7 Hz cutoff frequency

“Furniture” appearance with oak wood exterior

$650 budget. Increase due to oak materials.

Design Models:
With sage guidance and sanity checks from moderator “Mike P”, I dialed in the WinISD Pro model for the enclosure, port and filter characteristics. Using an 18.7 Hz cutoff frequency (modeled as a 2nd order butterworth) the cone excursion appears to behave well.

Construction:
The main legs need to be 2.25” thick to provide material for the angled dadoes and to support the heft of this enclosure. Calculations say this will weigh in at a solid 220 lbs. Since I’m frugal (ok, cheap!), I face glued 1x8 oak boards to 2x8 pine boards after surface planing . 16 pipe clamps produced about 40psi clamp pressure. This is a bit light but I used all my clamps. Titebond III glue was used. The extra boards in the stack are clamping cauls to help distribute the clamp force.

The center bracing structure is ¾” birch plywood glued with biscuits and Titebond III. A ¼” roundover bit in the router made smooth edges in these cutouts. The third leg was made by ripping a 1x8 oak board into three pieces and face gluing to form a solid, square post. The legs were ripped and jointed to make square, clean lines. In the picture below you can see the 3 main panels cut from ¾” MDF. The “v” shaped rail is glued and screwed to the front panel. This “v” rail receives the bracing and stiffens the front panel. I made this by gluing a 2x6 pine board to a ¾” plywood strip.

Dadoes proved to be trickier than I anticipated. My stacked dado blade fell short in the width of cut and depth of cut needs. In the end, I used my normal saw blade tilted at 45 degrees and took bites out until I achieved the width and depth.

I cut 2 plywood pieces to exactly the same outside dimensions of the leg spacing. This made jigging and assembling the framework less tedious.

Since this design requires an oak exterior, I glued ¼” oak veneered plywood to the ¾” MDF panels. Contact cement worked well for this bond. The 45 degree front panel is glued into the angled, 1” dadoes using Gorilla glue. This polyurethane glue was a good choice for these joints since it expands to fill voids and I like how it bubbled out on the inside. This added strength to the joint. Note, this glue also bubbled out on the oak veneer exterior too. For about an hour after gluing this front panel, I wiped the fresh, bubbling glue away from the oak with a rag saturated in lacquer thinner. The bracing assembly was also glued to the corresponding rail with Gorilla glue and screws.

Side panel and vent panel glued to the main assembly. Again, I’m using poly glue for the expansion properties. Since the assembly was still open and accessible, I attached the speaker wire using cable clamps and silicone sealant. I didn’t want the speaker wire vibrating later.

I made great strides with the assembly however I forgot to take pics. Here’s the enclosure assembly trimmed out with ¼” solid oak trim boards. The trim design portrays classic craftsman style. This recess in the top will house the sub plate amplifier. One detail I didn’t cover relates to the vent and the outside panel. I was worried the outside panel adjacent to the vent may vibrate so I reinforced with ½” diameter dowels pins. One of the last pictures in this posting shows the vent and pins. Before I assembled the outside panel, I drilled ½” diameter holes about 1.0” deep. I gorilla glued the dowels and left exactly 1.25” (vent width) of exposed dowel. I then glued the outside panel in place. With careful measurements, I located the center of the 3 dowels and marked this on the outside panel. I pilot drilled a 3/16” diameter hole through the outside panel, dowel, vent and into the bracing. The pilot depth is about 2.75”. A 4” long wood screw was driven through the panel, dowel, vent panel and into the bracing.

1” plywood works great for the plates that hold the driver and amp. I glued 1.25 x 1.50 pine boards around the panels to create a "shelf" to support the amp and driver plates. A dado would have worked better but the angles made this too challenging.

With the enclosure flipped over, a 12” saw blade worked great for locating the driver’s center position. A compass and careful jigsaw work opened up these holes.

I didn’t discuss the lid design but here’s how I built it: I had a remnant piece of 3/4” oak veneered plywood that I sized and clad the edges with ¼” x ¾” trim strips. I cut a 4” x 18” opening to allow the vent to breathe freely. Using 1.25” x 1.5” pine sticks, I assembled a “picture frame” to serve as the bones for the black grill cloth covering. Rare earth magnets from PE were epoxied into lid and legs to secure the top.

After cooking out in the sun for the morning and afternoon, I brought the enclosure inside to assemble. Here’s the CSS Trio 12 about to settle in.

I didn’t mention this earlier but I also purchased a new AV receiver and Blu-Ray player. To eliminate the potential of many possible failure points, I tested the sub with the old AV receiver since I could rely on this signal. So I hooked up this sub to the old receiver to test its operation.

Drum roll please…

Wow!!! This thing rocks!

I played the DVD “Master and Commander: Far Side of the World” and I forwarded to the opening battle scene. The cannon blasts were heard and felt in my chest. Feeling these blasts truly enhanced the movie experience. What was supposed to be a 5 minute “go” or “no-go” test turned into 2+ hours of thoroughly enjoying this movie! Like an addict, I kept replaying the actions scenes! This sub added a new dimension to the movie experience and I couldn’t be happier with the performance! The enclosure is rock solid as far as I can tell and I hear no port noises. After playing around with levels and crossover cutoffs, I found 80 Hz crossover and #4 out of 10 for the volume is the sweet spot. This sub is capable of delivering higher, clean output but I find it too distracting since this content “overpowers” the rest of the audio/visual presentation. During my exploration of other DIY builds, I’ve read many stories about “house shaking bass” and I took this with a grain of salt. As an engineer, I consider myself to be a fairly objective person and I can say in all honesty “this sub shakes my house”!

I’ve now upgraded the AV receiver and the Blu-Ray player and watched several movies. I absolutely love this sub. I have read many forums where post-build tuning and signal processing was required to compensate for room modes and other audio artifacts. I guess I got lucky that my sub worked straightaway. As much as my techie-side would like to measure and compare response data and evaluate room modes, I’m not finding the need. This sub exceeds expectations for sound and subaudible performance. An example: My family enjoys the Harry Potter movies so I played “The Order of The Phoenix”. In the scene when Harry is brought to “Grimmauld Place” and the building magically separates to expose the hidden “House of Black” the sound of the stone building moving was awe inspiring. The room and house shook (in a good way) and I was completely convinced this was exactly the sound and feel as if I were standing there.

There are 2 pending issues. The BASH 500w amp’s “Auto-On” feature does not work. It’s supposed to work like this: the amp hibernates after a period of time where no input signal is detected. Once an input signal is detected, the amp should turn on automatically. Mine goes to sleep but fails to wake up. I won’t bore you with all the troubleshooting details. After I was convinced the amp was faulty, I called PE and they confirmed this unit is defective. They are shipping a replacement.

Second issue: In the adjacent dining room, the sidelight windows next to the patio door have aluminum frames for screens. During certain high-energy low frequency effects, these screens rattle. I need to take them out and line the gap with tape to attenuate the vibration.

Comments about the driver:
I’ve studied reviews of many 12” drivers and I decided to go with the CSS Trio 12” driver. This modeled very well and the reviews were positive. A concern was raised by other reviewers regarding the stamped steel frame and the potential for vibration or structural failure. After inspecting and operating this driver, I believe the engineering and fabrication is solid. In my opinion, this driver is a great value. It delivers great performance at a good price. I am very happy with this driver.

Comments about the amplifier:
Sound quality and performance is great. I’ve observed nothing concerning regarding the performance. The auto-on feature does not work and PE is replacing this under warranty. I haven’t received the replacement yet so I can only speak to what I know with the original. I do hope the replacement works as advertised. I think this is a good value amplifier. If you are considering this amp for your project please read the forums regarding the factory set high pass filter. I believe the amp’s default HPF is set to 30Hz (or thereabouts) and if you’re building a sub it’s likely you’ll want the amp’s HPF much lower. There’s a 1-page manual (http://www.parts-express.com/pdf/300-752.pdf ) that’s shy on details. The “Bass Boost” tables provide the details you’ll need to modify the HPF to align with your WinISD model. In short, you can select and modify your amp’s HPF by changing 2 resistors on the pre-amp board. I chose the +1 dB bass boost at 27 Hz center frequency and 18.7 Hz cutoff. A screen shot from WinISD shows how I modeled this HPF. I remember reading forums where more than +2 dB bass boost was not advisable. I am comfortable soldering many things however this preamp modification project was outside my comfort zone. I am fortunate to have a coworker experienced in circuit board building and repair. He expertly de-soldered the 2 factory resistors and soldered-in the new R17 and R18 resistors (Thanks Kerry!).

6Sep11 Update: I called Parts Express on Monday, 29Aug and described the problem with the first amp. 2 days later I had a replacement amp sitting at my doorstep. This replacement amp works exactly as advertised (auto-on/off works great).

Total cost for this project ~$600. Note, I didn’t tally costs for the birch plywood (braces), ¾” oak plywood (lid), 1” plywood (driver and amp plates), glue, screws and polyurethane finish. These were leftovers from other projects. I estimate these materials would add another $60 to the cost of this project.

Final thoughts:
If you are reading this because you’re considering building a DIY sub, I say “go for it!” I was in your shoes too. This was my first sub build and it was a good experience. It took some time to understand WinISD’s inputs and outputs but the HTS forum and members were very helpful. After I converged on the box dimensions and modeled performance, the biggest challenge was construction of a wedge-shaped enclosure. Building a cube or rectangular shape with 90 degree joints would have been much easier. In the end, I feel I got a great performing sub at a great price.

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